Emulsion containing internally fogged photosensitive silver halide grains formed with an aqueous silver salt solution containing alkali metal iodide in thioether

ABSTRACT

A photosensitive emulsion containing internally fogged photosensitive silver halide grains having substantially no surface fog on the grains can be prepared by mixing a silver salt solution with a halide solution in a liquid reaction medium wherein the silver salt solution contains about 0.5 to about 7.0 mole percent iodide per mole of silver and mixing is carried out in the presence of at least 0.5 grams of a thioether silver halide solvent per mole of silver in the liquid reaction medium. Emulsions prepared can be employed in negative or direct-positive photographic materials. Such emulsions enable higher concentrations of sensitizing dyes to be employed on the photosensitive silver halide grains.

United States Patent 1 Miller, deceased 1 Oct. 23, 1973 EMULSION CONTAINING INTERNALLY FOGGED PI-IOTOSENSITIVE SILVER HALIDE GRAINS FORMED WITH AN AQUEOUS SILVER SALT SOLUTION CONTAINING ALKALI METAL IODIDE IN THlOETI-IER [7 5] Inventor: Jerry B. Miller, deceased, late of Webster, N.Y. by Carol K. Miller,

executrix [73] Assignee: Eastman Kodak Company,

Rochester, N.Y.

22 Filed: Feb. 3, 1972 21 Appl.No.:223,371

[52] US. CL; 96/107, 96/113, 96/114, 96/1 14.7 [51] Int. Cl. G03c 1/28 [58] Field of Search 96/107, 113, 114, L 96/1 14.7

[56] References Cited UNITED STATES PATENTS 3,S3l,288 9/1970 Jones 96/108 3,574,628 4/1971 Jones 96/107 Primary ExaminerNorman G. Torchin Assistant ExaminerWon H. Louie, Jr. Attorney-R. W. Hampton et al.

[57] ABSTRACT A photosensitive emulsion containing internally fogged photosensitive silver halide grains having substantially no surface fog on the grains can be prepared by mixing a silver salt solution with a halide solution in a liquid reaction medium wherein the silver salt solution contains about 0.5 to about 7.0 mole percent iodide per mole of silver and mixing is carried out in the presence of at least 0.5 grams of a thioether silver halide solvent per mole of silver in the liquid reaction medium. Emulsions prepared can be employed in negative or direct-positive photographic materials. Such emulsions enable higher concentrations of sensitizing dyes to be employed on the photosensitive silver halide grains.

8 Claims, No Drawings EMULSION CONTAININGJINTERNALL Y FOGGED PHOTOSENSITIVE SILVER 'HALIDE GRAINS FORMED WITH AN AQUEOUS SILVER SALT SOLUTION CONTAINING ALKALI METAL mixing steps. Another aspect'of the invention relates to silver'halide emulsions prepared employing} the described process which are useful in negative and/or direct-positive photosensitive materials. l 1 2. Description of the State of the Art I y l The preparation of surfacefogged photosensitive silver halide emulsions is'known, such as described in Illings'worth U.S. Pat. No. 3,501,305; 3,501,306 and 3,501,307 issued Mari 'l7, 1970. Preparations of internallyfogged emulsions generally have been carried out employing (l)exposure to light of a liquid photosensitive silver halide emulsion at some intermediate point during precipitation withtheresulting photolytically created fog specks being buried beneath the surface of the grains produced by additionalprecipitation or (2) incorporation of a reduction sensitizer early in the precipitation of the photosensitive silver halide with the resulting silver specks being buried within the grainby the remainder of the precipitation. There has been a continuing need, however, to provide a simplified method for preparation of internally fogged photosensitive silver halide which contains no significant surface fog on the silver halide grains;

"In preparation of photosensitive silver halide emulsions iodide compounds have been employed to provide a source ofiodide in the photosensitive silver halide producedhl-lowever, it is water soluble silver salt solution'employed in preparation of photosensitive sil- 2 silver halide grains which areinternally fogged and contain no significant surface fog.

1 SUMMARY OF THE INVENTION -It has been found according to the invention that preparation of a photosensitive emulsion, containing internally fogged photosensitive silver halide grains having substantially no surface fog on the grains, wherein a silver salt solution is mixed with a halide solution' in a liquid reaction medium can be carried out (a) using a silver salt solution, such as an aqueous silver nitrate solution, containing 0.5 to 7.0 mole percent ioverhalide because the halide would cause an undesired precipitate to form in thesilver salt solution-It has been considered disadvantageous, for example, to employ iodide in an aqueous silver nitrate solution before mixing with, for example, an aqueous potassium bromide solution.

Surprisingly, employing potassium iodide in the silver It. was surprisingly found, however, that thioether silver halide' solvents in the absence of some other component in preparation of photosensitive silver halide does not provide a desired internally fogged silver halide emulsion. This'is illustrated in following comparative Example 3.

There has been a continuing need to provide a simple process for providing an internally fogged photosensitive silver halide emulsion wherein the photosensitive dide per mole of silver in the silver salt solution and (b) carrying out the mixing step in the presence of at least 0.5 gramsof a thioethersilver. halidesolvent per mole of silver in the liquid reaction medium. This process provides a photosensitive silver halide emulsion which can be used in direct-positive photosensitive silver halide materials and/or negative photosensitive silver halide materials. The emulsions of the inventionand the method of preparing them enable the use'of surprisinglyhigh'concentrations of sensitizing dye'on the silver halide grains.

' DETAILED DESCRIPTION OF THE INVENTION Any suitable water soluble iodide compound or other source of iodide can be used in the practice of the invention'. Typical useful iodide compounds include the ammonium, potassium, lithium, sodium, cadmium and- /or strontium iodide compounds. Incarrying out the process of the invention, the water soluble iodide compound is employed in the desired silver salt solution at a concentration range of about 0.5 to about 7.0 mole per cent iodide per mole of silver in the silver salt solutionjDissolving of potassium iodide or other suitable iodide compound is 'usually more readily obtained when concentrated solutions of the silver salt are used, e.g. concentrated solutions of silver nitrate; For example, aqueous silver nitrate solutions greater than 2.0 molar enable dissolving of potassium iodide more readily. The concentration'of-iodide employed'in the silver 'saltsolution is,in addition to. any iodide uniformly present in the silver halide grains as mixed silver halide prepared accordingv to the invention, e.g. that iodide present in silver bromoiodide or silver chlorobromoiodide.

Various organic thioether silver halide solvents can be employed in the practice of the invention. Suitable organic. thioether silver halide solvents have greater solubility for silver halide, e. g., silver chloride, than water. More specifically, such thioether silver halide solvents are typically those which when utilized in aqueous solutions at 60 C. in 0.02 molar concentrations are capable of dissolving more than twice the amount by weight of silver halide than that which can be dissolved by water at 60 C.

A liquidreaction medium suitable in the process of the invention is typically an aqueous polymeric peptizer solution, such as an aqueous gelatin solution. A liquid reaction medium, such as an aqueous gelatin solution, has also been called in the art a kettle solution. The reactants are added to the kettle solution to form the desired silver halide. The liquid reaction medium is usually an aqueous solution but nonaqueous solvents, such as methanol and/or ethanol, can also be employed, if desired.

The concentration of thioether silver halide solvent utilized can be varied widely depending upon the particular thioether, the desired silver halide, the concentration of iodide employed, the reaction medium and the like. Mixing of the silver salt solution with a halide solution according to the invention is carried out in the presence of at least 0.5 grams of the described thioether silver halide solvent per mole of silver, e.g., about 0.5 grams to about 10 grams of thioether silver halide solvent per mole of silver in the liquid reaction medium.

Typical organic thioether silver halide solvents that can be utilized according to the invention contain at least one moiety wherein oxygen and sulfur atoms are separated by an ethylene radical, i.e., (-O-Cl-l Cl-l -S-). Generally the described thioether silver halide solvents have 1 to 3 thioether atoms, i.e., -S-, although silver halide solvents having more that 3 thioether atoms can be utilized. Suitable thioether silver halide solvents are described, for example, in U.S. Pat. No. 3,271,157 of McBride issued Sept. 6, 1966 and U.S. Pat. No. 3,574,628 of Jones issued Apr. 13, 1971.

Certain of the useful organic thioether silver halide solvents can be represented by the formulas:

wherein: r and m areintegers of to 4; n is an integer of l to 4; p and q are integers of 0 to 3; X is an oxygen atom O a sulfur atom S a carbamyl radical a carbonyl radical or a oxycarbonyl radical R and R are ethylene oxide radicals (-O-CH -CH Q and Z are hydroxy radicals (-OH), carboxy radicals, or alkoxy radicals (-O-alkyl) wherein the alkyl group has 1 to 5 carbon atoms; and Q and Z can also be substituents described for X linked to form a cyclic compound.

In one embodiment, the organic thioether silver halide solvent is a straight chain thioether, such as those represented by the formulae:

wherein r is an integer of l to 3 and R is an alkylene radical having 1 to 5 carbon atoms and is preferably ethylene (-CH CH In another embodiment, the organic thioether silver halide solvent is a cyclic organic thioether, i.e., such as those represented by the formula:

wherein s is an integer of l to 2 and R is as defined above.

The photosensitive silver halides which can be formed according to the invention include any of the photosensitive silver halides such as silver bromide, silver iodide, silver chloride, silver chlorobromide, silver bromoiodide, silver chlorobromoiodide and the like. Silver halide grains prepared according to the invention typically have a mean grain diameter, i.e., an average grain size in the range of about 0.1 to about 2 microns and typically about 0.25 to about 1 micron. Mean grain diameter, i.e., average grain size can be determined using conventional methods. The silver halides which are prepared according to the invention can be prepared using typical emulsion making procedures including single-jet procedures, double-jet procedures, procedures utilizing automatic proportional control means to maintain specified pAg and pH, procedures utilizing an increase in flow rates as described in Wilgus U.S. Pat. application Ser. No. 11,838 filed Feb. 16, 1970, hot nucleation procedures as described in Musliner U.S. Pat. application Ser. No. 31,351 filed Apr. 23, 1970 and the like.

The silver halide compositions made according to the invention are preferably monodispersed which comprise silver halide grains having a substantially uniform diameter. Generally, in such emulsions no more than about 5 percent by weight of the silver halide grains smaller than the mean grain size and/or no more than about 5 percent by number of the silver halide grains larger than the mean grain size vary in diameter from the mean grain diameter by more than about 40 percent. Preferred photographic emulsions prepared according to the process of the invention comprise silver halide grains at least 95 percent by weight of the grains having a diameter which is within 40 percent, preferably within about 30 percent of the mean grain diameter. The described uniform size distribution of silver halide grains is a characteristic of grains in monodispersed photographic silver halide emulsions. Silver halide grains having a narrow size distribution can be obtained by controlling the conditions at which the silver halide grains are prepared using a double-run procedure. In such a procedure the silver halide grains are prepared by simultaneously running an aqueous solution of a water soluble silver salt, for example, silver nitrate containing the described iodide compound, and a water soluble halide, for example, an alkali metal halide such as potassium bromide, into a rapidly agitated aqueous solution of a silver halide peptizer, preferably gelatin, a gelatin derivative or some other protein peptizer. The pH and the pAg employed in this procedure are interrelated. For example, changing one factor while maintaining the other constant at a given temperature can change the size frequency distribution of the silver halide grains which are formed. However, generally the temperature employed in the process of the invention is about 30 to about C., the pH is up to about 9, but preferably less than about 7, e.g. about 4 to about 7, and the pAg is controlled between about 7 and about 9.8. Procedures for preparing silver halide emulsions containing uniform particle size are described, for example, in an article entitled la:

Properties of Photographic Emulsion Grains," by Klein and Moisar, The Journal of Photographic Science, Vol. 12, 1964, pp. 242-251; an article entitled The Spectr al Sensitization of Silver Bromide Emulsions on Different Crystallographic Faces," by Markocki, The Jourml! of Photographic Science, Vol. 13, 1965, pp 85-89; an article entitled"Studies on Silver Bromide Sols, Part I. The Formation and Aging of Monodispersed Silver Bromide Sols, by Ottewill and Woodbridge, The Journal ofPhotographic Science, Vol. 13, 1965, pp..98l03; and an article entitled Studies on Silver Bromide Sols, Part 11. The Effect of Additives on the S01 Particles, by Ottewill and Woodbridge, The Journal of Photographic'Science, Vol. 13, 1965, pp. 104-107.

A range of silver'halide' peptizers can be employed in the practice of the invention. While these are generally gelatin, a gelatin derivative or some other proteinpeptizer, other silver halide peptizers are suitable such as cellulose'derivatives, polysaccharides and the like as well as synthetic polymeric'substances such as vinyl polymers described in l-louck U.S.Pat'. No. 3,062,674 issued Nov. 6,1962; Lowe U.S. Pat. No. 2,311,059 issued Feb. 16, 1943 and Belgian Pat. No. 727,604 published Mar. 31, 1969. l

The concentration of peptizer in a peptizer solution employed in the process of the invention is typically about grams to about 100 grams of the described peptizer per liter of solvent, e.g. per liter of water.

The photographic emulsions and elements prepared according to the invention can contain various colloids alone or in combination as vehicles or binding agents and in variouslayersSuitable hydrophilic materials include both naturally occurring substances such as proteins, for example, gelatin, gelatin derivatives, cellulose derivatives, polysaccharides such as dextran, gum arabic and the like; and synthetic polymeric substances such as water-soluble polyvinyl compounds like poly(- vinylpyrrolidone), acrylamide polymers and the like The described photographic emulsion layers and other layers of a photographic element employed in the practice of this invention can also contain, alone or in combination with hydrophilic, water-permeable col- ,loids, other synthetic polymeric compounds such as dispersed vinyl compounds such asin latex form and particularly those which increase the dimensional stability of thepho tographic materials. Suitable synthetic polymers include those described, for example, in U.S. Pat. No. 3,142,568 by Nottorf issued July 28, 1964; 3,193,386 by White issued July 6, 1965; 3,062,674 by Houck et al. issued Nov. 6, 1962; 3,220,844 by Houck et al. issued Nov. 30, 1965; 3,287,289 by Ream et al. issued Nov. 22, 1966; and 3,41 1,91 1 by Dykstra issued Nov. 19, 1968; particularly effective are those waterinsoluble polymers or latex copolymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates, those which have cross-linking sites which facilitate hardening or curing, those having recurring sulfobetaine units as described in Canadian Pat. No. 774,054 by Dykstra, and those described in U.S. Pat. No. 3,488,708 by Smith issued Jan. 6, 1970.

The photographic layers and other layers of a photographic element employed and described herein can be coated on a wide variety of supports. Typical supports include cellulose nitrate film, cellulose ester film, poly(vinyl acetal) film, polystyrene film, poly(ethylene terephthalate) film, polycarbonate film and related films or resinous materials, as well as glass, paper, metal and the like. Typically, a flexible support is em- 6 ployed, especially a paper support, which can be partially-acetylated or coated with baryta and/or an alphaolefin polymer, particularly a polymer of an alphaolefin containing 2 to 10 carbon atoms such as polyethylene, polypropylene, ethylenebutene copolymers and the like.

This invention may be used with elements designed for colloid transfer processes such as described in U.S. Pat. No. 2,716,059 by Yutzy et al.; silver salt diffusion transfer processes; color image transfer processes such as described in U.S. Pat. No. 3,087,817; 3,185,567 and 2,983,606 by Rogers, 3,253,915 by Weyerts 'et al., 3,227,550 by Whitmore et al., 3,227,551 by Barr et al., 3,227,552 by Whitmore and 3,415,644, 3,415,645 and 3,415,646 by Land, and U.S. Pat. Ser. Nos. 27,990 and 27,991, both filed Apr. 13, 1 970; and imbibition transfer processes as described in U.S. Pat. No. 2,882,156 by Minsk.

This invention may be used with elements designed for color photography, for example, elements containing color-forming couplers such as those described in U.S. Pat. No. 2,376,679 by Frohlich et al., 2,322,027 by Jelley et al., 2,801,171 by Fierke et al., 2,698,794 by Godowsky, 3,227,554 by Barr et al., and 3,046,129 by Graham et al.; or elements to be developed in solutions containing color-forming couplers such as those described in U.S. Pat. No. 2,252,718 by Mannes et al., 2,592,243 by Carroll et al. and 2,950,970 by Sch wan et al.; and in false-sensitized color materials such as those described in U.S. Pat. 'No. 2,763,549 by Hanson.

The silver halide emulsions of the invention can comprise electron acceptors which are referred to in some documents as desensitizers. The concentrations of the electron acceptors will vary with silver halide composition, average grain size, distribution of grain size and the like. In certain preferred embodiments good results are obtained when the electron acceptors are added to monodispersed photosensitive silver halide emulsions in concentrations of generally about 10 to about 500 milligrams per mole of silver and preferably about 50 to about 200 milligrams per mole of silver.

Generally, the electron acceptors or desensitizers in theemulsions of the invention are those compounds having a reduction potential or cathodic halfwave potential (E more positive than minus 1.0V. In certain embodiments useful electron acceptors also have an anodic halfwave potential more positive than plus 090V and preferably more positive than plus 1.0V.

The electrochemical potential measurements can be made with an approximately 10 molar solution of the dye in an electrolyte; for example, methanol which is 0.05 molar in lithium chloride. A dropping mercury electrode can be used for the cathodic measurement with the polarographic half-wave potential for the cathodic response most positive in potential designated E A pyrolytic graphite electrode can be used for the anodic measurement with the voltammetric half-peak potential for the anodic response most negative in potential designated E In each measurement, the reference electrode can be an aqueous silver-silver chloride (saturated potassium chloride) electrode at 20 C. Plus and minus signs are assigned to the potential values according to the IUPAC Stockholm Convention 1953. The B and E,- values so measured shall not include processes in which electron transfer is primarily the result of the presence in solution of the counter ion of a positively charged dye or other such chemical entities in solution that are not an integral part of, or attached to, the chromophoric system of the dye. A response of lesser current magnitude preceding the primary response, such as a prewave resulting from adsorption of the electrolysis product to the electrode surface, shall be excluded from designation as E, or E Electrochemical measurements of this type are known in the art and are described in one or more of the following reference texts: New Instrumental Methads in Electrochemistry, by Delahay, lnters cience Publishers, New York, New York, 1954; Polarography, by Kolthoff and Lingane, 2nd Edition, lnterscience Publishers, New York, New York, 1952; and Electrochemistry at Solid Electrodes, by Adams, Marcel] Dekker, Inc., New York, New York, 1969. t

In a preferred embodiment of this invention, the desensitizers are methine dyes, generally referred to as monomethine and/or polymethine dyes. Generally, these methine dyes include those which are useful in direct-positive silver halide emulsions as electron acceptors.

In certain preferred embodiments, the useful polymethine dyes of this invention can be characterized as containing at least one desensitizing nucleus. As used herein and in the appended claims, desensitizing nucleus" refers to those nuclei which, when converted to a symmetrical carbocyanine dye and added to a gelatin silver chlorobromide emulsion containing 40 mole percent chloride and 60 mole percent bromide, at a concentration of from 0.01 to 2.0 grams dye per mole of silver, cause by electron trapping at least about an 80 percent loss in the blue speed of the emulsion when sensitometrically exposed and developed 3 minutes in Kodak Developer D-l9 at room temperature. Advantageously, the desensitizing nuclei are those which, when converted to a symmetrical carbocyanine dye and tested as just described, essentially completely desensitize the test emulsion to blue radiation (i.e., cause a loss or more than about 90 to 95 percent of speed to blue radiation).

An especially useful class of electron-accepting compounds which can be used in the photographic silver halide emulsions of this invention is cyanine dyes, particularly imidazoquinoxaline dyes, such as described in Brooker et al., U.S. Pat. No. 3,43l,1 11 issued Mar. 4, 1969. Very good results are obtained with cyanine dyes containing an indole nucleus aromatically substituted in the 2 position, i.e., a cyanine dye containing a 2- aromatically substituted indole nucleus such as disclosed in U.S. Pat. No. 3,314,796 issued Apr. 18, 1967. One useful class of spectral-sensitizing, electron acceptors is the bis-( l-alkyl-2-phenylindole-3)trimethine cyanine described by Coenen et al., U.S. Pat. No. 2,930,694 issued Mar. 29, 1960. Another useful class of dimethine cyanine dyes of this type is described in British Pat. No. 970,601.

Still other classes of useful spectral-sensitizing electron acceptors are the cyanine and merocyanine dyes in which at least one nucleus and preferably two nuclei contain desensitizing substituents such as N e.g., 3,- 3-diethyl-6,6-dinitrothiacarbocyanine chloride, as shown in British Pat. No. 723,019.

The described spectral sensitizing electron acceptors are useful in producing reversal images.

The electron acceptors or desensitizers can be used in photosensitive silver halide emulsions of the invention in varying concentrations. However, such compounds are typically at concentrations in a range of about 50 milligrams to about 800 milligrams of the compound per mole of silver halide. Specific examples of suitable electron acceptors or desensitizers include 1, l '-dibutyl-4,4'-dipyridinium chloride,

Phenosafranine, and related halogen at dyes, as described in U.S. Pat. No. 3,501,309, including 1,1,3,3'-tetramethyl-2,2'-cyanine iodide, NBS 3,3'-diethylthiacyanine iodide, NBS

9-ethyl-3 ,3 '-dimethyl-4,5,4,5 '-dibenzothiacarbocyanine chloride, NBS

1,1-dimethyl-2,2'-cyanine iodide. NBS represents N-bromosuccinimide.

The silver halide grains prepared according to the invention contain no significant surface fog. Such emulsions contain only minimal developable surface fog sites wherein processing for 5 minutes at 27 C. in Kodak Developer DK-SO will provide a density of less than 0.4 and preferably less than 0.25. However, the surface of the silver halide grains of the invention can be chamically sensitized. Chemical sensitization, as employed herein, includes sensitization of the type described by Antoine Hautot and Henri Saubenier in Science et Industries Photographiques, Vol. XXVlll, January, 1957, pages [-23, and January, 1957, pages 57-- 65. Such chemical sensitization includes three major classes, viz., gold or noble-metal sensitization, sulfur sensitization such as by a labile surfur compound, and reduction sensitization, i.e., treatment of the silver halide with a strong reducing agent which does not appreciably fog the silver halide but introduces small specks of metallic silver into the silver halide crystal or grain.

Various exposure and development processes can be employed to provide a negative or positive image employing the photosensitive silver halide emulsions of the invention. The emulsions prepared according to the invention are typically, however, exposed imagewise and then developed in an internal silver halide developer. A typical internal developer has the following composition:

Water (50C) about 500 cc. N-methyl-para-aminophenol 2.0 grams sulfate (Elon) Sodium sulfite 90.0 grams Hydroquinone 8.0 grams Sodium carbonate, monohydrated 52.5 grams Potassium bromide 5.0 grams Potassium iodide 0.5 grams Water to make 1 liter In certain embodiments an image can be developed employing the emulsions of the invention utilizing a surface developer.

It is understood that the term surface developer" encompasses those developers which will reveal the surface latent image on a silver halide grain, but will not reveal substantial internal latent image in an internal image forming emulsion, and conditions generally used develop a surface sensitive silver halide emulsion. The surface developers can generally utilizeany of the silver halide developing agents or reducing agents but the developing bath or composition is generally substantially free of a silver halide solvent, such as water soluble thiocyanates, water soluble thioethers, thiosulfates, ammonia and the like, which will crack or dissolve the grain to reveal substantial internal image.

Typical silver halide developing agents which can be used in developing compositions for developing an image in an emulsion according to the invention in- 9 elude hydroquinones, catechols, aminophenols, 3- pyrazolidones, ascorbic acid and its derivatives, reductones, phenylenediamines and the likeor combinations of these. The developing agents can be incorporated in photographic elements containing emulsions of the invention wherein they are brought in contact with the silver halide after exposure; however, in certain embodiments they are preferably employed in a developing solution. l i

Generally, the'emulsions of the invention areemulsions-which can be made by asimple silver halide precipitation. Generally, the emulsions can be described as primitive silver halide emulsions which are substantially free of any chemically induced sensitivity 'on the surface of, the grain. Preferably the emulsions are those which can be defined as primitive emulsions which are those derived from precipitation of an alkali metal halide with a water soluble silver salt in the presence of a peptizer and are substantially free of any sulfur and- /or noble metal sensitization.

Normal spectral sensitizing dyes can be used conveniently to conferadditional sensitivity to the light sensitive silver halide emulsion of the invention. For instance, additional spectral sensitization can be obtained by treating the emulsion with a solution of a sensitizing dye in an organic solvent or the dye may be added inthe form of a dispersion as described in Owens et a]. British Pat. No. 1,154,781 issued June 11, 1969. For optimum results, the dye may either be added to the emulsion as a final step or at some earlier stage.

Sensitizing dyes useful in sensitizing such emulsions for negative images are described, for example, in Brooker et al. U.S. Pat. No. 2,526,632 issued Oct. 24, 1950'; Sprague u.s. Pat. No. 2,503,776 issued Apr. 11, 1950: Brooker et a1; U.S'. Pat. No. 2,493,748 issued Jan. 10, 1950; and Taber et al. U.S. Pat. No. 3,384,486 issued May 21, 1968. Spectral sensitizers which can be used include the cyanines, merocyanines', complex (triortetranuclear) merocyanines, complex (trior tetranuclear) cyanines, holopolar cyanines, styryls, hemi cyanines (e.g. enamine 'hemicyanines oxonols and hemioxonols. f

Dyes of thecyanine classes can containsuch basic nuclei as the thiazolines', 'oxazolines, pyrrolines, pyridines, oxazoles, thiazoles, selenazoles and imidazoles. Such nuclei can contain alkyl, alkylene, hydroxyalkyl, sulfoalkyl, carboxyalkyl, aminoalkyl and enamine groups and can be fused to carbocyclic or heterocyclic ring. systems either unsubstituted or substituted with halogen, phenyl, alkyl, haloalkyl, cyano, or alkoxy groups. The dyes can be symmetrical or unsymmetrical and can contain alkyl, phenyl, enamine or heterocyclic substituents on the methine or polymethine chain.

The merocyanine dyes can contain the basic nuclei mentioned above as well as acid nuclei such as thiohydantoins, rhodanines, oxazolidenediones, thiazolidenediones, barbituric acids, thiazolineones, and malononitrile. These acid nuclei can be substituted with alkyl, alkylene, phenyl, carboxyalkyl, sulfoalkyl, hydroxyalkyl, alkoxyalkyl, alkylamino groups, or heterocyclic nuclei. Combinations of these dyes can be used, if desired. In addition, supersensitizing addenda which do not absorb visible light can be included, for instance, ascorbic acid derivatives, azaindenes, cadmium salts, and organic sulfonic acids as described in McFall et al., U.S. Pat. No. 2,933,390 issued Apr. 19, 1960;

10 and Jones et al. U.S. Pat. No. 2,937,089 issued May 17, 1960.

The emulsions of the invention and the preparation enable the use of a surprisingly high concentration of sensitizing dye on the surface of the silver halide grains. The'concentration of dye is typically about 50 milligrams to about 800 milligrams per mole of silver halide. The use of spectral sensitizing dyes on the surface of the silver halide emulsions of the invention at these unusually high levels does not provide loss of the fogged properties of the silver halide. Moreover, in view of the fact that the process of the invention provides silver halide wherein the fog is internal, it is an-advantage of the emulsions in that they do not provide oxidative destruction of the fog due to oxygen attack during incubation or keeping. 1

Various silver salts can be employed in the practice of the invention in preparing the described silver halide grains. The silver salt is typically a water soluble silver salt, such as silver nitrate.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 This example illustrates the preparation of preferred emulsions according to the invention.

Silver bromoiodide gelatino emulsions having an average grain size of about 1.0 micron are prepared by adding an aqueous solution of potassium bromide and an aqueous solution of silver nitrate containing potassium iodide at a concentration described in Table I, simultaneously to a rapidly agitated gelatin solution also known as a kettle solution. The gelatin solution contains a thioether silver halide solvent at a concentration described in Table l. The mixing is carried out at a temperature of 50 C. over a period of 40 minutes at a pAg of 8.9. The resulting silver halide emulsions are washed position:

water, about (50C.) 500 cc. N-methyl-para-amino phen sulfate (Elon) 2.0 g. Sodium sulfite 90.0 g. Hydroquinone 8.0 g. Sodium carbonate, monohydrated 52.5 g. Potassium bromide 5.0 3.

Water to make 1 liter or 2 a. immerse in a surface bleach for 5 minutes. The

surface bleach composition is:

glacial acetic acid 1.8 cc. sodium hydroxide 0.8 g. potassium ferricyanide 3.18 g.

water to l litter b. develop 6 minutes in an internal image developer which is Kodak Developer D-19 containing 0.5

grams potassium iodide per liter. In each instance the resulting photographic element is fixed, washed and dried.

The silver halide emulsion composition variables and the results obtained are listed in following Table I.

TABLE I Mole Thioether Fog Values Emul- Kl in Kettle Developer: sion dissolved Solution l (2) No. in AgNO (g/M) Surface lnternal IA l.49 |(0.5) 0.04 0.70 18 1.49 l(2.0) 0.06 2.18 lC 1.49 l(2.0) 0.06 2.08 1D 0.75 ll( l .l) 0.05 2.00 IE L49 None 0.03 0.03 1 F 1.49 None 0.04 0.03

In Emulsion 1C the potassium iodide is added to the silver nitrate solution under red safe light conditions and stirred until a precipitate which is formed is dissolved. In the other described emulsions this step is carried out in white light.

The thioether designated as l is l,8-dihydroxy-3,6- dithiaoctane. The thioether designated as ll is 1,10- dithia-4,7,l 3 l 6-tetraoxacyclooctadecane.

It can be seen from the results of this table that the process of the invention employing both potassium iodide and the thioether provide an internal image emulsion which contains no significant surface fog on the silver halide grains which would enable development of a surface latent image.

EXAMPLE 2 This example illustrates the utility of the described emulsions for negative or direct positive materials.

To separate portions of internally fogged silver halide emulsions prepared as described in Example 1 are added dyes A and B atthe concentrations listed in Table 11. After digestion of the silver halide emulsions at 40 C. for l minutes, the emulsions resulting are coated, exposed and processed in a surface developer (6 minutes in Kodak Developer D-l9) or an internal developer (6 minutes in Kodak Developer D-l9 and 0.5 grams per liter potassium iodide).

The results obtained are listed in Table II.

TABLE II Surface Internal development devel. (reversal) (negative) Emulsion Dye relative Rel. rev. number (mg/M.) speed Dmi... speed Dmi... Dmnx.

1A None.... 100 .04 None .70 0.70 A (100 None .04 219 .04 0.44 A (200)- None .04 186 .04 0.22 B (100)- None .04 300 .04 0.55 B (200)- None .04 269 .04 0.45

1C None 148 .06 None 2. 08 2. 08 A (50)" None .04 83 .17 1.02 A (100)- None .04 105 .12 1.40 B (100)- None .05 112 .18 1.90 B (200) None .06 126 .13 1.14

113 None 155 .06 None 2.18 2.18 A (50 None .06 83 .16 2.20 A (100 None .06 174 .15 2. 00

1D None 41 .05 None 2. 00 2. 00 A (100)- None .07 525 .22 .90 A (500) None .07 363 .20 .60 B (100)- None .07 457 .14 1.38 B (200)- None .07 525 .12 1.26

Measured at 0.3 above minimum density. I

"Measured at a point corresponding to Dmaxminus Dm. divided by two.

It can be seen from the results of this table that it is suitable to employ the internally fogged silver halide emulsions of the invention with an electron-trapping dye and process the emulsion in an internal developer to provide a suitable reversal image.

EXAMPLE 3 This example illustrates that potassium iodide is required in the silver nitrate solution according to the invention.

The procedure set out in Example 1 is repeated with the exception that potassium iodide is omitted from the described silver nitrate solution. After processing, as described in Example 1, the following results are observed TABLE III Thioether Kl in Kl in Kl in (l) in AgNO Kettle Salt Kettle Solution Solution Solution FIG VAlues (glm) Mole Mole Mole Surface Internal 2.0 None None 2.48 0.05 .20

2.0 None 2.48 None 0.06 .08

2.0 L49 None None 0.06 2.18

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

What is claimed is:

1. In a method of preparing a photosensitive emulsion containing internally fogged, photosensitive silver halide grains having substantially no surface fog on said grains, comprising mixing an aqueous silver salt solution with an aqueous alkali metal halide solution on a liquid reaction medium containing a polymeric peptizer, said method being carried out in the absence of an intentional silver halide chemical sensitization step, the improvement wherein (a) said silver salt solution contains 0.5 to 7.0 mole percent iodide per mole of silver in said silver salt solution, and said mixing is carried out in the presence of at least about 0.5 gram to about 10 grams of a thioether silver halide solvent per mole of silver in the liquid reaction medium.

2. The method of claim 1 wherein said silver salt solution is an aqueous silver nitrate solution and said liquid reaction medium is an aqueous gelatino peptizer solution.

3. The method of claim 1 wherein said thioether silver halide solvent is l,8-di-hydroxy-3,o-dithiaoctane.

4. The method of claim 1 wherein said thioether is silver halide solvent is l,l0-dithia-4,7,l3,l6- tetraoxacyclooctadecane.

5. The process of claim 1 wherein pl-l during mixing of said solutions is controlled at less than about 7 and pAg is controlled about about 7 and about 9.8.

6. A method of preparing a photosensitive emulsion containing internally fogged, silver bromoiodide grains contains about 0.5 gram to about 10 grams of 1,8-dihydroxy-3,6-dithiaoctane or 1 l 0-dithia-4,7,l 3, l 6- tetraoxacyclooctadecane per mole of silver in said aqueous gelatino peptizer solution.

7. A photosensitive silver halide emulsion prepared by the process of claim 1.

8. A photosensitive silver halide emulsion prepared by the process of claim 6. 

2. The method of claim 1 wherein said silver salt solution is an aqueous silver nitrate solution and said liquid reaction medium is an aqueous gelatino peptizer solution.
 3. The method of claim 1 wherein said thioether silver halide solvent is 1,8-di-hydroxy-3,6-dithiaoctane.
 4. The method of claim 1 wherein said thioether is silver halide solvent is 1,10-dithia-4,7,13,16-tetraoxacyclooctadecane.
 5. The process of claim 1 wherein pH during mixing of said solutions is controlled at less than about 7 and pAg is controlled between about 7 and about 9.8.
 6. A method of preparing a photosensitive emulsion containing internally fogged, silver bromoiodide grains having substantially no surface fog on said grains comprising mixing an aqueous silver nitrate solution with an aqueous potassium bromide solution in an aqueous gelatino peptizer solution, said method being carried out in the absence of an intentional silver halide chemical sensitization step, the improvement wherein (a) said silver nitrate solution contains 0.5 to 7.0 mole percent potassium iodide per mole of silver in said silver nitrate solution, and said aqueous gelatino peptizer solution contains about 0.5 gram to about 10 grams of 1,8-dihydroxy-3,6-dithiaoctane or 1,10-dithia-4,7,13,16-tetraoxacyclooctadecane per mole of silver in said aqueous gelatino peptizer solution.
 7. A photosensitive silver halide emulsion prepared by the process of claim
 1. 8. A photosensitive silver halide emulsion prepared by the process of claim
 6. 